The paper summarizes the authors' major results achieved recently with their collaborators on the study of molecular Rydberg states and nonlinear spectral effects. The results include the findings of diversified nonlinear spectral effects, the recognition of new spectral regulations and their identification methods for molecular two-photon excitation spectra simplified by the mechanism of near-resonant enhancement, and proposals and demonstrations of manifold mechanisms for generating stimulated and coherent radiation from infrared to ultraviolet wavelength regions out of simple molecules or via them.The paper summarizes the authors' major results achieved recently with their collaborators on the study of molecular Rydberg states and nonlinear spectral effects. The results include the findings of diversified nonlinear spectral effects, the recognition of new spectral regulations and their identification methods for molecular two-photon excitation spectra simplified by the mechanism of near-resonant enhancement, and proposals and demonstrations of manifold mechanisms for generating stimulated and coherent radiation from infrared to ultraviolet wavelength regions out of simple molecules or via them.

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIEOct 28, 19920 citations

Nonlinear Spectroscopy

Wolfgang Demtröder

Springer eBooksJan 1, 20154 citations

Measurement principles for quantum spectroscopy of molecular materials with entangled photons

Luca Moretti, Esteban Rojas‐Gatjens, Lorenzo Uboldi +8 more

Nonlinear spectroscopy with quantum entangled photons is an emerging field of research that holds the promise to achieve superior signal-to-noise ratio and effectively isolate many-body interactions. Photon sources used for this purpose, however, lack the frequency tunability and spectral bandwidth demanded by contemporary molecular materials. Here, we present design strategies for efficient spontaneous parametric downconversion to generate biphoton states with adequate spectral bandwidth and at visible wavelengths. Importantly, we demonstrate, by suitable design of the nonlinear optical interaction, the scope to engineer the degree of spectral correlations between the photons of the pair. We also present an experimental methodology to effectively characterize such spectral correlations. Importantly, we believe that such a characterization tool can be effectively adapted as a spectroscopy platform to optically probe system-bath interactions in materials.Nonlinear spectroscopy with quantum entangled photons is an emerging field of research that holds the promise to achieve superior signal-to-noise ratio and effectively isolate many-body interactions. Photon sources used for this purpose, however, lack the frequency tunability and spectral bandwidth demanded by contemporary molecular materials. Here, we present design strategies for efficient spontaneous parametric downconversion to generate biphoton states with adequate spectral bandwidth and at visible wavelengths. Importantly, we demonstrate, by suitable design of the nonlinear optical interaction, the scope to engineer the degree of spectral correlations between the photons of the pair. We also present an experimental methodology to effectively characterize such spectral correlations. Importantly, we believe that such a characterization tool can be effectively adapted as a spectroscopy platform to optically probe system-bath interactions in materials.

arXiv:2304.07828The Journal of Chemical PhysicsAug 24, 202310 citations

Nonlinear spectroscopy of molecules

Kōichi Shimoda, Tadao Shimizu

Progress in Quantum ElectronicsJan 1, 197325 citations

Nonlinear Spectroscopy

Laser SpectroscopyJul 22, 20082 citations

Universal Scaling and Many-Body Resurrection of Polaritonic Double-Quantum Coherences

Maxim Sukharev

The ultrafast nonlinear optical response of molecular ensembles is fundamentally altered under strong light-matter coupling. To rigorously isolate the genuine many-body contributions, an exact time-domain field-subtraction protocol is developed within a fully non-perturbative Maxwell-Liouville framework explicitly incorporating the two-exciton manifold in real space and time. This approach reveals that while collective cavity delocalization drives the macroscopic nonlinear signal toward a severe harmonic cancellation (an effect termed "spectral starvation"), intrinsic many-body molecular interactions robustly resurrect genuine polaritonic double-quantum coherences (DQCs). This many-body resurrection is governed by a universal two-photon matching rule, $Δ_B + 4J = Ω_R$ , linking molecular anharmonicity ( $Δ_B$ ) to the macroscopic Rabi splitting ( $Ω_R$ ) and excitonic coupling ( $J$ ). Crucially, this resonance exploits the spatial mismatch between macroscopic polaritons and localized two-exciton pairs to break harmonic cancellation. For J-aggregates ( $J < 0$ ), this condition uniquely isolates the resonant many-body state below the dense manifold of localized dark states, protecting the macroscopic coherence from spatial fragmentation. This predictive framework establishes a direct phase diagram to engineer and protect optical nonlinearities across diverse strongly coupled platforms.The ultrafast nonlinear optical response of molecular ensembles is fundamentally altered under strong light-matter coupling. To rigorously isolate the genuine many-body contributions, an exact time-domain field-subtraction protocol is developed within a fully non-perturbative Maxwell-Liouville framework explicitly incorporating the two-exciton manifold in real space and time. This approach reveals that while collective cavity delocalization drives the macroscopic nonlinear signal toward a severe harmonic cancellation (an effect termed "spectral starvation"), intrinsic many-body molecular interactions robustly resurrect genuine polaritonic double-quantum coherences (DQCs). This many-body resurrection is governed by a universal two-photon matching rule, $Δ_B + 4J = Ω_R$, linking molecular anharmonicity ($Δ_B$) to the macroscopic Rabi splitting ($Ω_R$) and excitonic coupling ($J$). Crucially, this resonance exploits the spatial mismatch between macroscopic polaritons and localized two-exciton pairs to break harmonic cancellation. For J-aggregates ($J < 0$), this condition uniquely isolates the resonant many-body state below the dense manifold of localized dark states, protecting the macroscopic coherence from spatial fragmentation. This predictive framework establishes a direct phase diagram to engineer and protect optical nonlinearities across diverse strongly coupled platforms.

physics.chem-phCross-listedarXiv:2604.03423Apr 7, 20260 citations

Δ_B + 4J = Ω_R

, linking molecular anharmonicity (

Δ_B

) to the macroscopic Rabi splitting (

Ω_R

) and excitonic coupling (

J

). Crucially, this resonance exploits the spatial mismatch between macroscopic polaritons and localized two-exciton pairs to break harmonic cancellation. For J-aggregates (

J < 0

), this condition uniquely isolates the resonant many-body state below the dense manifold of localized dark states, protecting the macroscopic coherence from spatial fragmentation. This predictive framework establishes a direct phase diagram to engineer and protect optical nonlinearities across diverse strongly coupled platforms.